Effect of protease treatment on the baking quality of brown rice bread: From textural and rheological properties to biochemistry and microstructure

In this study, protease treatment of brown rice (BR) batters was investigated in order to evaluate its impact on the textural and baking properties of BR bread. The enzymatic treatment improved bread quality by significantly increasing specific volume (p < 0.05), while decreasing crumb hardness and chewiness (p < 0.05). Fundamental rheology and viscometry of batters revealed that protein hydrolysis induced lower complex modulus and initial viscosity, while phase angle was unaffected. Flour pasting properties were also affected, with a significant decrease in paste viscosity and breakdown (p < 0.05). Protein analysis of batters revealed that the enzymatic treatment induced the release of low molecular weight proteins from macromolecular protein complexes. In conclusion, a lower resistance to deformation of batters during proofing and in the early stages of baking as well as the preserved batter elasticity and the increased paste stability positively affected the breadmaking performance.     

Development and evaluation of rheological and bioactive properties of rice protein-based gels

The rice industry produces a large amount of by-products daily. In fact, it is estimated that approximately 100 million tons of rice residues and by-products are generated each year. However, new protein sources are demanded for human food because of the continuous increase in the global population coupled with the almost total inability to increase global food production.A rice protein concentrate (RPC), which is a by-product of the rice industry, and two different hydrolysates (RPH₂₅ and RPH₁₂₀) obtained from RPC, have been used in order to evaluate the potential of RPC to form a gel-like food product at three different pH values (2.0, 6.5 and 8.0). The gelation process was monitored and subsequently, mechanical spectra were obtained. In addition, protein interactions (ionic interactions, hydrophobic interactions, hydrogen bonds and disulphide bonds) were also determined in order to understand the gel structure. Finally, an antioxidant characterisation was carried out using three different reagents: DDPH, ABTS and Folin-Ciocalteu.A proper degree of hydrolysis and an optimal pH value seem to be key factors in the manufacturing of gels, showing a remarkable influence on both rheological properties and antioxidant activities.     

Physicochemical characterization and in-vitro digestibility of extruded rice noodles with different amylose contents based on rheological approaches

The physicochemical properties and in-vitro digestibility of extruded rice noodles with different amylose contents were characterized from a rheological point of view. Thermo-mechanical measurements showed that the rice flour with higher amylose contents exhibited greater stability to dual-mixing and higher degrees of starch gelatinization and retrogradation. In addition, greater elastic properties were clearly observed in the high amylose rice samples. The use of high amylose rice flour produced noodles with a harder texture, consequently contributing to reduced cooking loss. Furthermore, the rheological changes of extruded rice noodles were monitored in real time during the in-vitro starch digestion. The rice noodle digesta with higher amylose contents exhibited greater viscosities throughout the simulated oral-gastric-intestinal digestion steps. The flow behaviors of the rice noodle digesta consisted of the Power-law region and infinite shear plateau that were satisfactorily characterized by the Sisko model (R² > 0.99).     

Characterisation and functional properties of Australian rice protein isolates

Albumin, globulin, glutelin and prolamin fractions were isolated from an Australian rice variety (cv. Langi) and characterised by yield, protein content and molecular weight profile using both capillary electrophoresis (SDS-CE) and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The influence of pre-extraction enzymatic hydrolysis of starch and heating to 70 °C was also investigated, as was the extraction of the glutelin fraction without prior removal of the albumin and globulin fractions. Pre-extraction treatment affected mainly the albumin fraction, increasing dry matter yield but reducing protein content. SDS-CE was able to separate the protein fractions over a wider molecular weight range than SDS-PAGE, and the peaks from SDS-CE showed slightly higher molecular weight compared to equivalent bands from SDS-PAGE. The glutelin fraction extracted without prior removal of albumin and globulin fractions had different characteristics compared to those obtained by conventional extraction methods. Pre-extraction hydrolysis of starch did not significantly affect the emulsifying, foaming and gelling properties of extracted protein. Although rice glutelin had poor solubility, emulsifying and foaming properties in aqueous systems, it had good gelling properties which could be important for food applications.     

Thermal and rheological properties of brown flour from Indica rice

The thermal, paste and rheological properties of brown flours from four Indica rice subspecies with different amylose content were examined using Differential scanning calorimetry (DSC), Brabender Viscometer and rheometer. Peak, final and setback viscosities (p < 0.05) increased with increasing amylose content from Brabender micro Visco-Amylo-Graph (MVA), but the phase transition temperatures of brown rice flour from DSC (p < 0.05) decreased with increasing amylose content. Rheological properties were determined by steady shear, small amplitude oscillatory shear (SAOS) and thixotropic experiments. SAOS results showed a gel-like viscoelastic behavior with G′ higher than G″. Steady-shear results showed that the brown rice flour exhibited a non-Newtonian shear-thinning behavior and the flow curves can be well described by the Herschel-Bulkley model. The upward-downward rheograms showed that brown rice flour gel, except IR-1, had a hysteresis loop, indicating a strong thixotropic behavior.     

Water mobility,rheological and textural properties of rice starch gel

Three rice starches from indica (TNuS19), japonica (TNu67) and waxy (TCW70) were used as samples to investigate the water mobility, viscoelasticity and textural properties of starch gels using pulsed nuclear magnetic resonance (PNMR), dynamic rheometer and texture analyzer. The spin–spin relaxation time (T₂), showed water mobility of starch gels was detected with starch concentrations 10–30%. Generally, the TNuS19 and TNu67 at ≥20% showed two components (T_2a and T_2b) in water mobility, where T_2a and T_2b related to solid-like and liquid-like water molecules in starch gels, respectively. However, the TCW70 over the concentrations examined had only T_2b component, higher than those of corresponding TNuS19 and TNu67. The storage (G′) and loss (G″) moduli of starch gels were in the order of TNuS19 > TNu67 > TCW70. Texture analyzer analysis indicated that TNuS19 had higher hardness, stickiness and adhesiveness than did the TNu67 and TCW70, and changed significantly with the starch concentration increase. The value of T_2b was highly correlated with physical properties of starch gels, especially with dynamic rheological parameters. It is suggested that amylose content may play a major role to influence the water mobility of starch gels which affects the specific viscoelasticity and textural properties of starch gels.     

Optimization of microwave-assisted extraction of rice bran protein and its hydrolysates properties

Microwave-assisted extraction (MAE) was applied for extracting rice bran protein with a response surface methodology (RSM). The optimal condition was 1000 W of microwave power, 90 s of extraction time, and a solid to liquid ratio of 0.89 g rice bran/10 mL of distilled water. The protein yield of MAE was higher than that of alkaline extraction (ALK) by about 1.54-fold (P < 0.05), while the protein digestibility was similar. The protein hydrolysates (PHs) with at different degrees of hydrolysis (DH) (5.04, 10.37 and 15.04%) were produced by alcalase. The molecular weight (MW) of the rice bran protein concentrates (RBPC) and the PHs ranged between <11 kDa and 100 kDa. The excessive enzymatic hydrolysis resulted in a negative effect on water and oil absorption capacities. The PHs with DH15.04% acted as the strongest DPPH radical scavenger, ferric reducing agent, and also metal ion chelator (P < 0.05). However, a DH of 5.04% was sufficient for improving the functional properties of RBPC, especially foam ability and the emulsion activity index. This study suggests that the desirable properties of rice bran protein can be controlled with enzymatic modification.     

Antioxidative properties of partially purified barley hordein, rice bran protein fractions and their hydrolysates

Antioxidative properties of proteins from barley and rice bran and their hydrolysates were examined. Three major hordein fractions of barley, B, C and D hordeins, were partially purified by gel filtration. Albumin, globulin, prolamin and glutelin fractions of rice bran were fractioned by the Osborne method. Hydrolysates of these protein fractions were prepared by digesting with pepsin followed by trypsin. Antioxidant properties in terms of antioxidative activity against linoleic acid peroxidation and reducing activity without the lipid adjuvant were investigated. The globulin fraction from rice bran protein revealed the strongest antioxidative activity throughout the incubation time of 7 days (p ≤ 0.05). The albumin fraction of rice bran protein showed the highest reducing activity (6964 μmol of Fe²⁺) followed by globulin, prolamin, glutelin and hordein fractions with activities of 2904, 2017, 1809 and 1333 μmol of Fe²⁺, respectively (p ≤ 0.05). Partially purified C hordein exhibited the highest reducing activity compared with B and D hordeins. Protein hydrolysates obtained after digestion with pepsin and trypsin exhibited much greater antioxidative, as well as reducing, activities than those from before digestion.     

Microstructure, fundamental rheology and baking characteristics of batters and breads from different gluten-free flours treated with a microbial transglutaminase

Gluten is a fundamental component for the overall quality and structure of breads. The replacement of the gluten network in the development of gluten-free cereal products is a challenging task for the cereal technologist. The functionality of proteins from gluten-free flours could be modified in order to improve their baking characteristics by promoting protein networks. Transglutaminase (TGase) has been successfully used in food systems to promote protein cross-linking. In this study, TGase was investigated for network forming potential on flours from six different gluten-free cereals (brown rice, buckwheat, corn, oat, sorghum and teff) used in breadmaking. TGase was added at 0, 1 or 10 U/g of proteins present in the recipe. The effect of TGase on batters and breads was evaluated by fundamental rheological tests, Texture Profile Analysis and standard baking tests. Three-dimensional elaborations of Confocal Laser Scanning Microscopy (CLSM) images were performed on both batters and breads to evaluate the influence of TGase on microstructure. Fundamental rheological tests showed a significant increase in the pseudoplastic behaviour of buckwheat and brown rice batters when 10 U of TGase were used. The resulting buckwheat and brown rice breads showed improved baking characteristics as well as overall macroscopic appearance. Three-dimensional CLSM image elaborations confirmed the formation of protein complexes by TGase action. On the other side, TGase showed negative effects on corn flour as its application was detrimental for the elastic properties of the batters. Nevertheless, the resulting breads showed significant improvements in terms of increased specific volume and decreased crumb hardness and chewiness. Under the conditions of this study, no effects of TGase could be observed on breads from oat, sorghum or teff. Overall, the results of this study show that TGase can be successfully applied to gluten-free flours to improve their breadmaking potentials by promoting network formation. However, the protein source is a key element determining the impact of the enzyme.     

Wheat flour non-starch polysaccharides and their effect on dough rheological properties

Wheat (Triticum aestivum L.) flour is able to form dough with unique rheological properties that allow bread making. It is well known that wheat protein content affects dough rheological properties, but there is not enough evidence about the role of other minor flour constituents. One such minor constituent is non-starch flour polysaccharides, which are mainly pentosans formed by a xylopyranosyl linear chain branched with arabinofuranosyl residues. Their spatial distribution and branching pattern can affect their relationship with gluten forming proteins and thus influence their functional properties, the dough rheological properties, and thereby the flour baking quality. In this study the content and structural characteristics of non-starch polysaccharides were investigated, as well as their influence on some dough physicochemical parameters. Five different wheat flours samples milled from Uruguayan wheat varieties with diverse rheological and breadmaking properties were used in this study. Water soluble flour polysaccharides were extracted and the amount of pentosans was determined by the orcinol-HCl method. The pentoses composition was determined before and after acidic hydrolysis of the water soluble polysaccharide fractions by GC. No free pentoses were detected in any of the assayed flour samples, so the pentoses composition found in the hydrolyzed samples was attributed to the non-starch water soluble polysaccharides. Water unextractable non-starch polysaccharides were determined by difference between the total and the soluble non-starch polysaccharides flour content.An improved method for the quantification of water extractable and non-extractable non-starch polysaccharides, using baker's yeast, was developed. Using this method, total and soluble non-starch polysaccharides content could reliably be determined both in whole flour and in pentosans enriched fractions. Free monosaccharide content was in the range from 0.03% to 0.06% (w/w), while the arabinose/xylose (Ara/Xyl) ratios varied from 0.8 to 1.4 in soluble non-starch polysaccharides and from 0.7 to 0.9 in total non-starch polysaccharides. The different Ara/Xyl ratios found for water extractable and unextractable arabinoxylans clearly indicates different substitution degrees in the polymers. Analysis of the dough rheological parameters in relation to the water soluble and non-soluble non-starch polysaccharides and the Ara/Xyl ratios from different wheat varieties was performed. A clear relation between some of these parameters could be inferred, since a direct relationship between total unextractable (AXi) content and resistance of dough to extension (P), as well an inverse relationship between the same parameter and dough extensibility (L) were observed. These results suggest that the flour non-starch polysaccharide content, as well the Ara/Xyl ratios may be used as additional parameters to estimate some of the wheat flours dough properties.     

Comparison of functional and structural properties of native and industrial process-modified proteins from long-grain indica rice

Rice proteins, as a cheap plant protein source from the by-products of rice dreg processing, could potentially replace commonly used proteins such as soy and whey proteins in selected food products. In this study, the functional properties, surface hydrophobicity (H₀), sulfhydryl and disulfide bond contents, thermal properties, as well as secondary structures of native rice endosperm protein (REP) and processed rice dreg protein (RDP) extracted from long-grain indica rice, were compared. RDP was found to have a higher solubility associated with its relatively higher emulsifying and foaming properties than REP, as well as its water/oil holding capacity, although it was a denatured protein. The emulsifying properties were dependent on the solubility and H₀, while solubility was also related to the disulfide bond contents. Distinct differences in H₀, thermal properties, and disulfide bond contents between REP and RDP could be due to the conformational changes, as the industrial processing steps in the production of rice syrups caused an increase in β-turns at the expense of β-sheets and random coils of REP, leading to the unfolding of β-sheets into higher-ordered supramolecular structures for RDP, which could be responsible for its better functional properties.     

Optimization of rheological properties of gluten-free pasta dough using mixture design

The rising demand of gluten-free products for celiac people has led to important technological research on the replacement of the gluten matrix in the production of high quality gluten-free foods. The objective of this work was to evaluate the effect of composition (hydrocolloids, water, and proteins) on the rheological and textural properties of gluten-free dough used for producing pasta based on corn-starch and corn flour. Extensibility and rheological properties of gluten-free pasta dough were studied. Rising protein or gum contents produced a marked increase of deformation at break. However protein content was negatively correlated with breaking force. The increase in gums content produced an increase in storage and loss moduli (G′, G″). G′ was always larger than G″ with a small increase of both moduli with frequency. The mechanical relaxation spectrum was predicted from dynamic oscillatory data using the broadened Baumgaertel–Schausberger–Winter model. Application of a mixture design allowed finding the optimal composition to achieve the desirable textural properties using response surface methodology. A formulation containing 35.5% water, 2.5% gums, 4.7% proteins, 42.8% corn-starch, 10.7% corn flour, 1% NaCl, and 2.8% sunflower oil led to the highest values of G′, breaking force, and extensibility according to the optimization analysis performed.     

Effect of preparation conditions on composition and sensory aroma characteristics of acid hydrolyzed rice bran protein concentrate

Hydrolysates were prepared from rice bran protein concentrate (RBPc) in paste form (P-RBPc), or as spray-dried (S-RBPc) or freeze-dried (F-RBPc) powder by acid hydrolysis with aqueous 0.5N HCl at 95 °C for 12 or 36 h. The forms of the protein raw material had only a slight influence over the sensory aroma characteristics of the liquid hydrolysates. The liquid hydrolysate (S-H-RBPc-12) prepared from S-RBPc with hydrolysis time of only 12 h could produce the desirable aromas as to a similar extent as that of 36 h. In order to demonstrate the effect of drying method on the composition and aroma characteristics, a representative S-H-RBPc-12 was converted into a powder by freeze- and spray-drying techniques. Sensory analysis indicated that the spray-dried powder had higher cracker-like and salty aroma intensities and received a higher overall liking score compared to the freeze-dried hydrolysate powder.     

Differences in functional properties and biochemical characteristics of congenetic rice proteins

Proteins in brown rice (BR), white rice (WR) and rice bran (RB) were extracted from the same paddy rice and investigated for their components, functional properties and chemical characteristics by SDS-PAGE methodology. BR and WR proteins possessed a poor solubility under weak acid conditions due to a high content of glutenin and richness in higher molecular-weight (MW) protein fractions. Rice bran protein contained significantly lower molecular-weight components (MWs < 50 kDa) than those in WR and BR. Nitrogen solubility, foaming and emulsification properties of their rice protein preparations were affected not only by pH (3–11), but also by the concentrations of NaCl (0.4–2.0%) and sucrose (4.0–20.0%). All of them, particularly rice bran protein, had favorable functional properties in the medium with a high salt or sugar concentration. Therefore, they have a good potential for development in the food industry.     

Effect of shear rate on microstructure and rheological properties of sheared wheat doughs

Structure formation in dough systems is the result of an interplay between processing conditions and subsequent interactions in the protein phase. These interactions can be both of a covalent (disulfide bonds) and physical nature and occur at all length scales.     

Effect of soluble dietary fibre addition on rheological and breadmaking properties of wheat doughs

The aim of this experimental work was to evaluate the effect of inulin addition on the rheological properties of common wheat doughs and bread quality. Three commercial fructan products of different number average degree of polymerisation (DPn) were used (DPn = 10 for inulin ST; DPn = 23 for inulin HP and HP-gel). Inulin contents from 2.5 to 7.5% on dry matter (wheat flour plus inulin) were used. Dough rheological properties were investigated using farinograph and dynamic rheological measurements. Upon addition of dietary fibre (DF), significant increase in mixing time and stability, and decrease in water absorption were recorded. Inulin ST exerted greater effect on water absorption than HP products.     

Temperature during grain ripening affects the ratio of type-II/type-I protein body and starch pasting properties of rice (Oryza sativa L.)

The starch and protein properties of rice grain are important factors for sake brewing and these properties are reported to be influenced by temperatures during grain ripening. Amylose content, nitrogen content, protein composition, pasting properties measured by a Rapid Visco Analyser (RVA), and their relationship to temperatures during ripening were investigated in a rice cultivar, Yamadanishiki, which was grown under various conditions in the same experimental field. The average temperature after heading was significantly correlated with amylose content and RVA properties, but not with nitrogen content. Under high temperatures during ripening, a decrease in prolamin, which accumulated in type I protein body (PB-I), and an increase in glutelin, which deposits in type II PB (PB-II), were recognized. The ratio of PB-II/PB-I and RVA pasting temperatures were distinctly increased as the temperature became higher. High temperatures during grain ripening would lead to difficulties in digesting steamed rice grains by Aspergillus oryzae, together with ease in digesting rice protein. The average temperature of 11–20 days after heading showed a higher correlation coefficient than that of 1–10 or 21–30 days, implying that temperatures during the middle stage of grain development would be important in determining the rice component that relates to brewing properties.     

Changes in gelatinization and rheological characteristics of japonica rice starch induced by pressure/heat combinations

Rice starch suspensions of 10% dry matter (DM) were treated by heat (0.1 MPa at 20–85 °C) or pressure/heat combinations (100–600 MPa at 20, 40 and 50 °C) for 15 min to investigate their gelatinization and rheological characteristics. The maximum swelling index of about 12 g water per gram of DM was obtained by thermal treatment at 85 °C, meanwhile, that of 7.0 g was observed by 600-MPa pressurization at 50 °C. The higher temperatures or pressures resulted in the higher degrees of gelatinization. Furthermore, treatments of 0.1 MPa at 85 °C, 500 MPa at 50 °C and 600 MPa at various temperatures caused complete gelatinization of rice starch. The consistency index (K) and storage modulus (G′) dramatically increased from 70 °C or 400 MPa. The G′ values were higher in pressure-treated samples than those in thermal-treated samples. Therefore, an application of pressure/heat combinations as a processing method to improve the quality of rice starch products would be possible.     

Protein-starch matrix microstructure during rice flour pastes formation

Scanned electron microscopy results revealed that the ability of forming a hair-like network (protein-starch matrix) as well as its rigidity constitutes to the conveying of the net pasting viscosities of flour. The formation of such network contributed to protecting starch granules integrity, resulted in increasing the resistance of rice paste to shear and thus increasing rice flour paste viscosity. Results also suggest that protein structural integrity and the nature of starch-protein bonding affected rice flour pasting mechanism formation.